The present invention relates to a variable focus camera capable of varying a focal magnification according to a photographer's wish and, more particularly, to a variable focus camera having an external view finder constituted by an optical system separate from that of a photographing lens.
For example, when a variable focus camera such as a lens shutter camera (e.g., a zoom camera) having an external view finder constituted by an optical system separate from that of a photographing lens is to be designed, a field magnification of the finder must be interlocked with an extension amount of the photographing lens for changing a magnification. Since the lens arrangement of the photographing zoom lens is different from that of the finder, the extension amounts of these lenses for changing a magnification are different from each other. If a magnification adjusting lens (magnification variable element) is moved in proportion to the extension amount of the photographing lens, the size of an object to be actually photographed differs from a field of view observed through the finder.
For this reason, in a conventional camera, in order to compensate for a difference in magnification change rate due to a difference in arrangement of the photographing lens and the finder lens, a rotational motion of a cam barrel for extending the photographing lens is transmitted to the finder through a gear train or the like, so that a correction cam plate inside the finder is moved by the cam barrel at a predetermined rate. Thus, the moving rate of the magnification adjusting lens of the finder is corrected by a member driven by the correction cam plate.
FIG. 8 shows the relationship between displacements of the photographing lens and the finder magnification adjusting lens and a rotation angle of the cam barrel in a conventional camera. The lens displacement is plotted along the ordinate, and the rotation angle of the cam barrel is plotted along the abscissa. The left end of the abscissa corresponds to a wide-angle end, and the right end thereof corresponds to a telescopic end. The photographing lens consists of front and rear component lenses, which are respectively indicated by FC and RC in FIG. 8. The finder is indicated by FD. As can be seen from FIG. 8, the photographing lens and the magnification adjusting lens of the finder have different displacements with respect to the rotation angle of the cam barrel. Since the displacement of the finder is not linearly changed with respect to the rotation angle of the cam barrel, the displacement of the finder magnification adjusting lens with respect to the rotation angle of the cam barrel is compensated for using the above-mentioned cam mechanism.
However, in such a correction structure between the photographing lens and the finder, since the correction cam plate itself is very small, precise machining is required, and a correction error becomes very large. Therefore, the size of an object to be actually photographed is largely different from the size (framing) of a field of view observed through the finder.
Meanwhile, if an electronic flash is attached to the variable focus camera, the radiation angle of the electronic flash must be changed in accordance with the extension amount of the photographing lens. However, although the finder must be corrected with considerable precision, as described above, the electronic flash need only be adjusted roughly. In addition, the electronic flash requires a certain strength in an interlocking mechanism with the cam barrel.
In the conventional camera comprising the external view finder and the electronic flash, two interlocking mechanisms, i.e., the high-precision interlocking mechanism of the finder and the interlocking mechanism of the electronic flash, which does not require high precision but requires a predetermined strength, must be arranged. For this reason, the number of components is increased, and an assembly process is complicated, resulting in an increase in manufacturing cost. In addition, the camera may frequently malfunction.